(1) Field of the Invention
The present invention relates to an assembly for automatically readjusting the air gap of a clutch or brake apparatus actuated by electromagnetic and spring forces.
(2) State of the Prior Art
Various assemblies for automatically readjusting the air gap of a clutch or brake apparatus that is actuated by electromagnetic and spring forces are known. Assemblies of this type are advantageous in that a uniform air gap will produce uniform operating conditions, i.e. uniform actuation times and improved positioning accuracy of the clutch or brake members. Furthermore, the user of such a clutch or brake apparatus will then not have to readjust the air gap, since the air ga is readjusted automatically.
One known type of readjusting assembly is known form EP-A1-54 734. However, this automatic readjusting assembly has the disadvantage of torque being transferred from a shaft to an armature plate through two annular springs or lamellas operating in series. One of the annular springs transmits torque from a flange hub connected to the shaft to an entrainment ring. An axially acting entrainment connection connects the entrainment ring to the armature plate. However, the entrainment connection does not transfer torque between the entrainment ring and the armature plate. The entrainment ring is connected to the armature plate for purposes of transmitting torque with the second annular spring. This arrangement of an automatic readjusting assembly suffers from the disadvantage that the distance the first annular spring must travel will increase with wear, so that it becomes increasingly difficult for a magnetic coil of the clutch or brake apparatus to reposition the entrainment ring for automatic readjustment against a frictional engagement which may exist between the shaft and the entrainment ring. This problem can be remedied by a locking mechanism acting on the shaft and the entrainment ring, but such a remedy involves substantial manufacturing expenses.
Another assembly for readjusting the air gap of a clutch or brake apparatus is known from DE-A-2 135 821. The arrangement disclosed therein uses axially movable bolts in connection with leaf springs in order to transfer torque from a hub on a shaft of a clutch or brake unit to an axially movable armature plate. However, the readjustment in this arrangement takes place at at least three points simultaneously.